There has been a great deal of interest in developing better and more efficient methods for storing energy for applications such as radio communication, satellites, portable computers, and electric vehicles to name but a few. Accordingly, there has been recent concerted efforts to develop high energy, cost effective batteries and electrochemical capacitors having improved performance characteristics.
Rechargeable or secondary cells are more desirable than primary (non-rechargeable) cells since the associated chemical reactions which take place at the positive and negative electrodes of the battery are reversible. Electrodes for secondary cells are capable of being regenerated (i.e., recharged) many times by the application of an electrical charge thereto. Numerous advanced electrode systems have been developed for storing electrical charge. Concurrently, much effort has been dedicated to the development of electrolytes capable of enhancing the capabilities of electrochemical cells.
Electrolytes are typically either liquid electrolytes as found in conventional wet cell batteries or solid films as are available in newer, more advanced battery systems. Each of these systems have advantages, though they have inherent limitations which make them unsuitable for particular applications. Liquid or aqueous electrolyte systems have heretofore been preferred over other systems as the ionic conductivity of aqueous electrolytes are significantly higher than their solid counterparts. Moreover, liquid electrolytes can more completely encircle the electrodes providing greater surface contact and hence improved electrochemical performance.
While liquid electrolytes are currently preferred over their solid counterparts, liquid electrolytes continue to have certain inherent limitations which make them unsuitable in various applications. For example, upon repeated cycling of a rechargeable battery, electrolytes tend to promote the formation of a passivation layer on electrode surfaces exposed to the electrolyte. This is particularly true of conventional potassium hydroxide (KOH) electrolytes. Moreover, certain electrode materials such as oxide containing electrode materials, have generally poor conductivity in conventional electrolyte systems, and hence the power density of energy storage systems into which such electrodes are incorporated is lower than optimal. Improvements in both of these areas could substantially increase performance of electrochemical cells.
Accordingly, there exists a need to improve current electrolyte systems so as to catalyze the electrode surface to diminish or minimize the passivation process and improve the rechargeability of the electrode. Moreover, improved electrolyte systems should be capable of improving conductivity and hence increasing power density of energy storage systems employing electrode materials with inherently poor conductivity.